He added that the explosion took place at 4:38 a.m. and that 200 to 250 kilograms of explosives were used in the blast.

"I was offering morning prayers along with two other colleagues on the rooftop of the police station at the time of the explosion," said one police constable, who was present at the time of the attack. "We heard a blast and suddenly found ourselves on the ground in rubble."

The Pakistani Taliban has claimed responsibility for the explosion.

Senior Khyber-Pakhtunkhwa Minister Bashir Ahmad Bilour -- who himself has escaped numerous attempts on his life by the Taliban in recent years -- visited the site minutes after the incident.

He urged all political parties to take a unified stand against terrorism.

"It is strange that some people still say this is not our war and someone else's war," he said. "A single party or the government alone can’t control it. All parties and people should be united to overcome the threat."

Residents of the neighboring area said the government and its security agencies were failing to ensure people's safety.

"Usually we see tight security arrangements which are further increased during night hours," said one nearby resident, who did not want to be named.

"But we don’t know how this bomber came amid tight security and hit the building. This is a key question. There is an order to shoot civilians if they don’t stop at a checkpoint. But why was this bomber not stopped at any checkpoint? Where were the security agencies?"

The blast was the latest in a number of attacks on Pakistani security forces following the May 2 raid by elite U.S. forces, which killed Al-Qaeda leader Osama bin Laden in the Pakistani city of Abbotabad.